2.21 Supercapacitors

Increasing demands for clean and renewable energy have stimulated intensive efforts to develop efficient energy storage technologies. Since the first commercialization of electrochemical supercapacitors by SOHIO and NEC, their configurations have been remarkably developed from electric double-layer capacitors to pseudocapacitors and then to hybrid capacitors. The performance of supercapacitors are strongly dependent on materials used as electrolytes and electrodes. Three types of electrolytes are employed, namely, aqueous electrolytes, organic electrolytes, and ionic liquids. Furthermore, electrode materials play a critical role in supercapacitors. Carbon-based materials are mainly used as double-layer capacitive electrodes and transition metal oxides/sulfates and conducting polymers as pseudocapacitive electrodes. Furthermore, supercapacitors have been applied to various electronic devices.